The invention relates to a datacarrier for detachable coupling to a terminal for data exchange between the terminal and the datacarrier, the datacarrier comprising a read/write memory and inhibiting means, arranged for inhibiting or enabling reading and/or writing in the memory by the terminal. The invention also relates to a method for writing into such a data carrier and to an integrated circuit for use in such a datacarrier.
A datacarrier of this kind is known from U.S. Pat. No. 3,971,916. The cited Patent describes several possibilities for storing inhibit information. One possibility consists in that for each use the memory is continuously addressed from the beginning, the complete addresses being compared with fixed addresses in two comparators, said fixed addresses denoting, for example the beginning and the end of an inhibited zone. These addresses are fixed in advance during the manufacture of the data carrier. Instead of a comparator, use can also be made of a counter which counts down a number of inhibited addresses. The number and the starting point, for example the address zero, are again fixed during manufacture of the card. Another possibility of inhibiting given memory locations from overwriting consists in that an additional bit is stored in each memory location during the write operation, said bit inhibiting the relevant memory location against overwriting. However, in that case it is also impossible to overwrite these memory locations if it were desirable to do so. Thus, this known data carriers is intended specifically intended for a very specific application. Therefore, different data carriers must be designed for each specific application.
U.S. Pat. No. 4,211,919 describes a data carrier in which the memory section is subdivided into three zones. The first zone contains data which is secret, can be used only within the data carrier, and cannot be overwritten. The second zone is freely available for writing and reading from or to the environment, it being necessary to transmit correct passwords in advance in order to write and read in this zone, depending on given protective information. This password information is stored in the third zone of the data carrier in which no writing but exclusively reading is possible. The limit addresses for the individual zones are also contained in the third zone and cannot be modified any longer after initialization of the data carrier.